Lowepro Mini Trekker AW Vs. Slingshot 300

Hello to all, I am looking for some information on both of these bags. The main reason I am looking at these two is because I believe I could keep my EF 70-200 f/2.8 IS mounted on my 50D and ready for use at say the zoo with the family. I was leaning towards the Slingshot as I could easily get the camera and shoot. I realize the weight with one strap could be an issue. I now see Bryan has a link to the Mini Trekker at a good discount from Adorama. It makes it tempting. I think that both hold the about same amount of gear. The Mini Trekker having two straps is most likely more comfortable for longer periods of time, but it does not have the quick access of the Slingshot. I would like to get some of your thoughts on the issue. Thank you in advance for the help.
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